Core drilling (or core sampling) includes obtaining core samples of subterranean formations at various depths for various reasons. For example, a retrieved core sample can indicate what materials, such as petroleum, precious metals, and other desirable materials, are present or are likely to be present in a particular formation, and at what depths. In some cases, core sampling can be used to give a geological timeline of materials and events. As such, core sampling may be used to determine the desirability of further exploration in a particular area.
Wireline drilling systems are one common type of drilling system for retrieving a core sample. In a wireline drilling process, a core drill bit is attached to the leading edge of an outer tube or drill rod. A drill string is then formed by attaching a series of drill rods that are assembled together section by section as the outer tube is lowered deeper into the desired formation. A core barrel assembly is then lowered or pumped into the drill string. The core drill bit is rotated, pushed, and/or vibrated into the formation, thereby causing a sample of the desired material to enter into the core barrel assembly. Once the core sample is obtained, the core barrel assembly is retrieved from the drill string using a wireline. The core sample can then be removed from the core barrel assembly.
Core barrel assemblies commonly include a core barrel for receiving the core, and a head assembly for attaching the core barrel assembly to the wireline. Typically, the core barrel assembly is lowered into the drill string until the core barrel reaches a landing seat on an outer tube or distal most drill rod. At this point a latch on the head assembly is deployed to restrict the movement of the core barrel assembly with respect to the drill rod. Once latched, the core barrel assembly is then advanced into the formation along with the drill rod, causing material to fill the core barrel.
One potential challenge can arise due to the interaction between the core barrel assembly and the drill string. For example, when the drill string is spinning, the inertia of the core barrel assembly can exceed the frictional resistance between the mating components such that the head assembly rotates at a lower rate than the drill rod or fails to rotate and remains stationary. In such a situation, the mating components can suffer sliding contact, which can result in abrasive wear.
Often it may be desirable to obtain core samples at various depths in a formation. Furthermore, in some cases, it may be desirable to retrieve core samples at depths of thousands of feet below ground-level, or otherwise along a drilling path. In such cases, retrieving a core sample may require the time consuming and costly process of removing the entire drill string (or tripping the drill string out) from the borehole. In other cases, a wireline drilling system may be used to avoid the hassle and time associated with tripping the entire drill string. Even when using a wireline drilling system, tripping the core barrel assembly in and out of the drill string is nonetheless time-consuming.
Accordingly, there are a number of disadvantages in conventional wireline systems that can be addressed.
There is a further need for core barrel head assemblies that provide improved tripping speed during descent into a drill string. Thus, there is a need for core barrel head assemblies that include mechanisms for (a) allowing standing fluid to pass through an inner tube for purposes of reducing drag during tripping of the head assembly into a hole while also (b) preventing drilling supply fluid from passing into the inner tube and damaging a core sample.
There is still a further need for core barrel head assemblies that provide for improved fluid control during all drilling conditions. Thus, there is a need for core barrel head assemblies that include mechanisms for reliably creating pressure change signals that are detectable by a drill operator and for ensuring fluid communication between a drill rig and a drill bit, particularly during “lost circulation” conditions when it is crucial to avoid a loss of fluid pressure.
Conventional core barrel head assemblies are not equipped with mechanisms for—and are incapable of—meeting all of these needs in a single assembly configuration. Instead, multiple configurations are required, thereby increasing the costs and complexity of manufacturing, inventory logistics, and operator training. Accordingly, there is a need in the pertinent art for a single core barrel head assembly configuration that is configured to provide for both improved tripping speed and improved fluid control under all drilling conditions.
An operator of a conventional core barrel head assembly typically relies upon deployment of a valve piston through an indicator bushing to generate a pressure signal that indicates a drilling position has been achieved. However, this pressure signal can only occur after the latch retracting case drops (following deployment of the latch mechanism). However, under non-ideal drilling conditions, such as those that occur during angled drilling, under adverse pump conditions, at excessive drilling depths, and/or under adverse ground conditions, there may be insufficient inertia or pressure to effect deployment of the valve piston. Thus, there is a need for alternative means for ensuring that latch deployment occurs, particularly under adverse drilling conditions.